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Arizona Chris
Joined: 20 Dec 2014
Posts: 69
Location: Arizona
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| Question on Tris setting when using SDA and SCL hardware.... |
 Posted: Sun Jun 14, 2015 6:58 pm |
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Hello all,
hopefully not too silly of a question. I'm writing interface drivers for an i2c digital device, and as of right now, I'm using "fast_io" and set the tris settings for each port in the main program. But when using the 877a hardware I2C ports (C3, C4) I can see you would use "output" for SCL, but since SCA is bidirectional, what to do?
The test program for the driver runs fine if I omit the fast io, and let CCS set the ports. is there a general rule here? I want to import my mini test program (no tris defined) into the main program which has fast_io and all tris defined. I guess I could leave the tris C out for now?
#use I2C(master, sda=PIN_C4, scl=PIN_C3, slow) |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Jun 14, 2015 7:59 pm |
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| Arizona Chris wrote: |
I can see you would use "output" for SCL, but since SCA is bidirectional,
what to do?
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No, the 16F877A data sheet says both pins must be set as inputs:
| Quote: |
9.4.2 OPERATION
Selection of any I2C mode, with the SSPEN bit set,
forces the SCL and SDA pins to be open-drain, provided
these pins are programmed to inputs by setting
the appropriate TRISC bits. |
Data sheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/39582C.pdf
| Arizona Chris wrote: |
But when using the 877a hardware I2C ports (C3, C4)
#use I2C(master, sda=PIN_C4, scl=PIN_C3, slow)
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The #use i2c() line above will use software i2c. To make the compiler
use hardware i2c, you have to add FORCE_HW to that line (and use
the hardware i2c pins).
| Arizona Chris wrote: |
I want to import my mini test program (no tris defined) into the main
program which has fast_io and all tris defined. I guess I could leave the
tris C out for now?
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You can still use fast i/o with a set_tris_c() statement. Just make sure you
set pins C3 and C4 to be inputs in that statement. |
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Arizona Chris
Joined: 20 Dec 2014
Posts: 69
Location: Arizona
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| i2cpins |
| Posted: Sun Jun 14, 2015 8:28 pm |
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THANK YOU PCM, I am having so much fun getting the code up and running on my digital compass, Im using the Adafruit HMC5883 break out board, and its totally awesome - has all the 3.3 to 5v conversion, and get this - is 9 bucks each! got it working in short order, now making the program optimized.
Chris |
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